The present invention relates to a process and an apparatus for leak testing a package.
European patent application 85.200.130.4 describes a method of leak testing vacuum packages. According to this method the vacuum package is placed in a sheet-like and air-tight wrapper, after which superatmospheric pressure is applied to the outside of the wrapper. This causes the wrapper to fit closely around the vacuum package. The small space remaining between the wrapper and the package is then sealed from the surrounding space, after which in this space the change of pressure is measured for a given period of time. A pressure variation is an indication of that the package leaks.
This prior art method is suitable for leak testing complete packages, e.g. vacuum-packed coffee, in which leaks may occur throughout the surface of the package.
In many packages such as jars or bottles made of glass or of a thermoplastic synthetic material, leak detection is only required where the jar or bottle is closed by a separately provided cover, screw cap or other closing element. For testing these types of packages, the prior art method of leak testing the complete package and therefore placing the package completely in a sheet-like wrapper is too laborious and time-consuming.
In another commercially sold testing apparatus, a bottle closed by a closing element can be leak tested by placing a bell over the closing element. With its lower edge, the bell rests on the shoulder of the bottle. Disposed along the lower edge of the bell is a specifically provided sealing ring, e.g. an inflatable O-ring. After inflating the O-ring, a seal of the bell against the shoulder of the bottle is obtained. An overpressure to a few bar or a vacuum is applied to the space between the bell and the bottle, which space is closed. When after some time the pressure in the closed space has changed, this may indicate that the closure of the bottle leaks.
This method is slow, owing to the relatively large volume in the bell to which, for each measurement, a pressure or a vacuum must be applied again. The repeated inflation of the O-ring is an additionally required step. Moreover, the seal between the bell and the bottle by means of an O-ring is less reliable, namely for two reasons. The first reason is that there is a rather great pressure differential over the O-ring (vacuum or overpressure at the inside and atmospheric pressure at the outside). The second reason is that the rather stiff O-ring is less able to adjust to the contours of the bottle, in particular when these contours are provided with a profile such as ribs, reliefs etc., or when the surface of the bottle shows roughnesses such as dents, grooves, etc. Consequently, this method is also unsuitable for rapidly and reliably testing closures of packages.